linux-kernel - [PATCH v4 2/6] PCI: dwc: Don't poll L2 if QUIRK_NOL2POLL_IN

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Message-Id: <20250822084341.3160738-3-hongxing.zhu@nxp.com>
Date: Fri, 22 Aug 2025 16:43:37 +0800
From: Richard Zhu <hongxing.zhu@....com>
To: frank.li@....com,
	jingoohan1@...il.com,
	l.stach@...gutronix.de,
	lpieralisi@...nel.org,
	kwilczynski@...nel.org,
	mani@...nel.org,
	robh@...nel.org,
	bhelgaas@...gle.com,
	shawnguo@...nel.org,
	s.hauer@...gutronix.de,
	kernel@...gutronix.de,
	festevam@...il.com
Cc: linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	imx@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Richard Zhu <hongxing.zhu@....com>,
	Frank Li <Frank.Li@....com>
Subject: [PATCH v4 2/6] PCI: dwc: Don't poll L2 if QUIRK_NOL2POLL_IN_PM is existing in suspend

Refer to PCIe r6.0, sec 5.2, fig 5-1 Link Power Management State Flow
Diagram. Both L0 and L2/L3 Ready can be transferred to LDn directly.

It's harmless to let dw_pcie_suspend_noirq() proceed suspend after the
PME_Turn_Off is sent out, whatever the LTSSM state is in L2 or L3 after
a recommended 10ms max wait refer to PCIe r6.0, sec 5.3.3.2.1 PME
Synchronization.

The LTSSM states are inaccessible on i.MX6QP and i.MX7D after the
PME_Turn_Off is sent out.

To support this case, don't poll L2 state and apply a simple delay of
PCIE_PME_TO_L2_TIMEOUT_US(10ms) if the QUIRK_NOL2POLL_IN_PM flag is set
in suspend.

Signed-off-by: Richard Zhu <hongxing.zhu@....com>
Reviewed-by: Frank Li <Frank.Li@....com>
---
 .../pci/controller/dwc/pcie-designware-host.c | 34 +++++++++++++------
 drivers/pci/controller/dwc/pcie-designware.h  |  4 +++
 2 files changed, 28 insertions(+), 10 deletions(-)

diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
index 1e130091d62a0..85740400a8d0d 100644
--- a/drivers/pci/controller/dwc/pcie-designware-host.c
+++ b/drivers/pci/controller/dwc/pcie-designware-host.c
@@ -1017,15 +1017,29 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
 			return ret;
 	}
 
-	ret = read_poll_timeout(dw_pcie_get_ltssm, val,
-				val == DW_PCIE_LTSSM_L2_IDLE ||
-				val <= DW_PCIE_LTSSM_DETECT_WAIT,
-				PCIE_PME_TO_L2_TIMEOUT_US/10,
-				PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
-	if (ret) {
-		/* Only log message when LTSSM isn't in DETECT or POLL */
-		dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n", val);
-		return ret;
+	if (dwc_quirk(pci, QUIRK_NOL2POLL_IN_PM)) {
+		/*
+		 * Add the QUIRK_NOL2_POLL_IN_PM case to avoid the read hang,
+		 * when LTSSM is not powered in L2/L3/LDn properly.
+		 *
+		 * Refer to PCIe r6.0, sec 5.2, fig 5-1 Link Power Management
+		 * State Flow Diagram. Both L0 and L2/L3 Ready can be
+		 * transferred to LDn directly. On the LTSSM states poll broken
+		 * platforms, add a max 10ms delay refer to PCIe r6.0,
+		 * sec 5.3.3.2.1 PME Synchronization.
+		 */
+		mdelay(PCIE_PME_TO_L2_TIMEOUT_US/1000);
+	} else {
+		ret = read_poll_timeout(dw_pcie_get_ltssm, val,
+					val == DW_PCIE_LTSSM_L2_IDLE ||
+					val <= DW_PCIE_LTSSM_DETECT_WAIT,
+					PCIE_PME_TO_L2_TIMEOUT_US/10,
+					PCIE_PME_TO_L2_TIMEOUT_US, false, pci);
+		if (ret) {
+			/* Only log message when LTSSM isn't in DETECT or POLL */
+			dev_err(pci->dev, "Timeout waiting for L2 entry! LTSSM: 0x%x\n", val);
+			return ret;
+		}
 	}
 
 	/*
@@ -1041,7 +1055,7 @@ int dw_pcie_suspend_noirq(struct dw_pcie *pci)
 
 	pci->suspended = true;
 
-	return ret;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(dw_pcie_suspend_noirq);
 
diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
index 00f52d472dcdd..4e5bf6cb6ce80 100644
--- a/drivers/pci/controller/dwc/pcie-designware.h
+++ b/drivers/pci/controller/dwc/pcie-designware.h
@@ -295,6 +295,9 @@
 /* Default eDMA LLP memory size */
 #define DMA_LLP_MEM_SIZE		PAGE_SIZE
 
+#define QUIRK_NOL2POLL_IN_PM		BIT(0)
+#define dwc_quirk(pci, val)		(pci->quirk_flag & val)
+
 struct dw_pcie;
 struct dw_pcie_rp;
 struct dw_pcie_ep;
@@ -504,6 +507,7 @@ struct dw_pcie {
 	const struct dw_pcie_ops *ops;
 	u32			version;
 	u32			type;
+	u32			quirk_flag;
 	unsigned long		caps;
 	int			num_lanes;
 	int			max_link_speed;
-- 
2.37.1